Production of gas suitable for use as town gas



United States Patent 3,104,957 PRODUCTION 65 GAS SUITABLE FOR USE ASTOWN GAS Hubert Thomas Porter, Arthur Knowles Renshaw, and

Peter Thomas White, all of Snnbury-on-Thames, England, assignors to TheBritish Petroleum (Company Limited, London, England, a Britishjoint-stock corporation No Drawing. Filed Mar. 11, 1958, Ser. No.720,537 Claims priority, application Great Britain Mar. 29, 1957 6flaims. (Cl. 48-197) This invention relates to the production of gassuitable for use as town gas from hydrocarbon fractions of petroleumorigin.

Traditionally, town gas has been obtained from the carbonisation ofcoal, but it has also been proposed to prepare it from petroleumfractions. \Vhen using petroleum fractions as starting materials, it isparticularly advantageous economically if the process used produces oneor more other valuable hydrocarbon products at the same time, andaccordingly, the present invention has among its objects to provide aprocess in which both town gas and a normally-liquid product suitablefor use in gasoline production or as a source of aromatics are produced.

According to the present invention, a fraction of petroleum originconsisting of or containing non-aromatic hydrocarbons and boiling withinthe gasoline or naphtha range is contacted at elevated temperature witha dehydrogenation and dehydrocyclisation catalyst under conditions suchthat a normally-liquid product with a higher aromatic content than thefeedstock and a hydrogen-rich gas are produced, and the calorific valueof the hydrogenrich gas is reduced to a value appropriate to the use ofthe gas as a town gas by dilution with a gas of lower calorific value.The gas of lower calorific value may contain noncombustible gases forexample carbon dioxide and nitrogen.

In a preferred form of the invention, the light hydrocarbon fraction iscontacted with a fluidised or moving bed of catalyst which iscontinuously or intermittently withdrawn from the reaction zone,regenerated in a stream of gas consisting principally of oxygen andnitrogen, and returned to the reaction zone, the flue gas from thecatalyst regeneration process being used to reduce the calorific valueof the hydrogen-rich gas.

A particularly suitable process for producing a higheraromatic contentproduct and a make of hydrogen-rich gas from the said hydrocarbonfraction is one using a catalyst consisting essentially of chromiumoxide supported on alumina carried out at a pressure of up to 50p.s.i.g. (including atmospheric pressure or below) and without recycleof the hydrogen-rich gas produced or addition of extraneous hydrogen.The temperature range is from 4-50 to 580 C. and the space velocity from0.1 to 1.0 v./v./hr. of liquid feedstock. The chromia on aluminacatalyst may contain a minor proportion of one or more promoters forexample a rare earth or mixture of rare earths, bismuth, boron,germanium or nickel, preferably in combination wiht an alkali metal,such as potassium. Another particularly effective pro- 'ice motor is aminor proportion of a spinel for example cobalt chromite, copperchromite, zinc titanate, or iron chromite, either as such or in the formof the naturallyoccurring ore chrome ironstone.

Preferably a substantial proportion of the feedstock boils below 100 C.,particularly preferred feedstocks being a light straight-run distillatesuch as a light gasoline or a light relatively aromatic-free fraction ofa catalytic reformate, for example a reformate obtained from a processusing a platinum containing catalyst.

The normally-liquid product may be used in gasoline or as a source ofaromatics, and the process conditions may be varied according to the usefor which the product is intended. Increased severity increases the makeof gas and the octane number of the liquid product but reduces theliquid yield. When carrying out the process for the production of townsgas and material for use in gasoline, the yields of gas and liquid andthe octane number of the liquid product must be balanced against eachother. On the other hand, when producing towns gas and a liquid productto be used as a source of aromatics, the decrease in overall liquidyield with increased severity may be advantageous rather thandisadvantageous. This is because the yield of aromatics by weight offeed rises to a maximum with increased severity and thereafter stayssubstantially constant, although the overall liquid yield continuer, todecrease by conversion of olefins and parafiins to gas. Under theconditions of pressure and space velocity stated above, the maximumyield of aromatics occurs at about 525- 570 C. It is preferred tooperate at the upper end of this range since, without affecting theyield of aromatics, an increased quantity of hydrogen-rich gas can beproduced for conversion to town gas.

The specification for an acceptable town gas is laid down by the gasboards, and may include a preferred range for calorific value, specificgravity, and hydrogen content. Since an important combustibleconstituent of the hydrogen-rich gas is the hydrogen itself, these threevalues are interdependent and dilution to reduce the calorific valuedecreases the hydrogen content and increases the specific gravity. Anyof these values, which can be determined by standard tests, maytherefore be used as a guide to determining the degree of dilutionrequired.

The invention is illustrated by the following examples.

EXAMPLE 1 A light gasoline was contacted in the vapour phase with afluidised bed of catalyst consisting of 10% chromia on alumina, promotedwith 1% of cerium oxide and 1% of potassium oxide (the percentages beingby weight of catalyst stable at 1020 F.) under conditions set out inTable 1 below. The vapours after having been freed from catalyst dust,were compressed in two stages to p.s.i.g. and passed to a productrecovery system in which a hydrogen-rich gas and a normally liquidfraction were separated by means of an absorber, a debutaniser and are-run column. The hydrogen-rich gas was taken off overhead from theabsorber, and the normally liquid fraction was taken oil overhead fromthe re-run column.

3 The fluidised catalyst reactor was associated in conventional mannerwith a catalyst'regenerator using air as the regenerating gas. Theprocess conditions for the reactor and regenerator are set out in Table1 below.

Inspection data on the light gasoline feed and the normally liquidfraction or product taken off overhead from the re-run column, are givenin Table 2 below.

Table 2 Test. 1 Feed Product ASTM Distillation, 0.:

FBP 103 120 Specific gravity (1) 60 F./60 F 0. 676 O. 765 Octane number,research clear." 57 98 Aromatics, percent vol 2 48 Bromine No 0. 4 40Sulphur, percent wt 0.015 0.007

From Table 2 it will be seen that a high-volatility gasoline fraction of98 research octane number (clear) is a product of the process. At thesame time, products having the general characteristics of a town gaswere obtained by diluting the hydrogen-rich gas taken ofi overhead fromthe absorber with cooled regenerator flue gas. For a town gas with acalorific value of 500 B.t.u./ cu. ft, 100 volumes of dry absorber gaswere mixed with 47.8 volumes of dry flue gas. Dry absorber gas and dryflue gas were also mixed in the required proportions to give a producthaving a specific gravity of 0.51.

Inspection data on the gases are set out in Table 3 below.

Table 3 Mixture Mixture Absorber Regenerto give to give gas, ator flue500 gas with percent gas, Btu. sp. gr.

vol. percent gas, 0.51,

v01. percent percent vol vol.

trace 1 .1 0 .3 0 .3

Total 100 .0 100 .0 100 .0

Gross CV, B.t.u./eu. ft. 730 500 555 Sp. gr. (Air=1) 0 .34 1.03 0.56 0

EXAMPLE 2 A light gasoline was contacted with a fixed bed of catalystconsisting of 10% of chromia on alumina promoted with 1% of cerium oxideand 1% of potassium oxide (the percentages being by weight of catalyststable at 1020 F.) under the following conditions:

Temperature 560 C., 1040 F. Pressure Atmospheric. Space velocity 0.2v./v./hr. Recycle gas None.

Processing period 5 hours.

Details of the feed and the liquid product are set out in Table 4 below.

T able 4 Light gasoline 61.2 ON (Res) Clear (05-112 0.)

Feed

Hydrocarbon Type Analysis atcs The table shows a gain in aromatics of28% by weight of feedstock. At the same time there was produced 2350s.c.f. of gas per barrel of feed, or 320 lbs. per 1000 lbs. of feed.This gas contained 67% by volume of hydrogen. A further 60 lbs. of gasper 1000 lbs. of feed was taken oii overhead from the stabiliser used todebutanise the liquid product. The two gases were combined to give a gaswith a density of 0.520 g./l. at 0 C. and 760 mm. Hg (0.40 specificgravity) and a calorific value of 833 B.t.u./cu. ft. The combined gaseswere diluted with an inert gas consisting principally of nitrogen andhaving a specific gravity of approximately 1 in proportion to give afinal gas with a density of 0.7 g./l. at 0 C. and 760 Hg (0.54 specificgravity) and a calorific value of 620 B.t.u./cu. ft. The yield of thisgas per 1000 lbs. of light gasoline feedstock was 12,400 cu. it.

We claim:

1. A process for the production of town gas and an aromatic-enrichedproduct comprising contacting a relatively aromatic-free petroleumfraction boiling Within the range encompassed by the gasoline andnaphtha range in a reaction zone with a dehydrogenation anddehydrocyclization catalyst consisting essentially of chromium oxidesupported on alumina at a temperature of from 450 C. to 580 C., at apressure not in excess of 50 p.s.i. ga., and in the absence of addedhydrogen to the reaction zone to produce an aromatic-enriched productand a make of hydrogen-rich gas, recovering a normally liquidaromatic-enriched product and a hydrogen-rich gas, regenerating thespent dehydrogenation and dehydrocyclization catalyst in a regenerationzone by contacting same with a stream of oxygen-containing gas,recovering from the regeneration zone the regenerated catalyst forre-use in the contacting zone and a flue gas having a lower calorificvalue than said hydrogen-rich gas, and combining the recovered line gaswith the hydrogen-rich gas to reduce the calorific value of saidhydrogen-rich gas to a value appropriate to the use of the formedblended gas as a town gas.

2. A process in accordance with claim 1 wherein the temperature in thecontacting zone is firom 525 C. to 570 C.

3. A process as claimed in claim 1 wherein a substantial proportion ofthe feedstock boils below C.

4 A process as claimed in claim 3 wherein the feed- References Cited inthe file of this patent stock is a straight-run, light gasoline. UNITEDSTATES PATENTS 5. A process as claimed in claim 3 wherein the feedstockis a light relatively aromatic-free fraction of a it: 21 2 Catalyflcrfiformafe- 5 2,488,027 Page Nov. 15, 1949 6. The process of clann 1wherem the catalyst 111 said 54 77 Leger F 13 1951 contacting zone is ina fluidized bed, and catalyst is con- 2,690,963 Herbst Oct. 5, 1954tinuously withdrawn from the reaction zone; regenerated 2,707,147Shapeleigh Apr. 26, 1955 in said regeneration zone and returned to thecontacting 10 2,849,383 Hirschler Aug. 26, 1958 Zen 2,894,826 StengleJuly 14, 1959

1. A PROCESS FOR THE PRODUCTION OF TOWN GAS AND AN AROMATIC-ENRICHEDPRODUCT COMPRISING CONTACTING A RELATIVELY AROMATIC-FREE PETROLEUMFRACTION BOILING WITHIN THE RANGE ENCOMPASSED BY THE GASOLINE ANDNAPHTHA RANGE IN A REACTION ZONE WITH A DEHYDROGENATION ANDDEHYDROCYCLIZATION CATALYST CONSISTING ESSENTIALLY OF CHROMIUM OXIDESUPPORTED ON ALUMINA AT A TEMPERATURE OF FROM 450*C. TO 580*C., AT APRESSURE NOT IN EXCESS OF 50 P.S.I. GA., AND IN THE ABSENCE OF ADDEDHYDROGEN TO THE REACTION ZONE TO PRODUCE AN AROMATIC-ENRICHED PRODUCTAND A MAKE OF HYDROGEN-RICH GAS; RECOVERING A NORMALLY LIQUIDAROMATIC-ENRICHED PRODUCT AND A HYDROGEN-RICH GAS, REGENERATING THESPENT DEHYDROGENATION AND DEHYDROCYCLIZATION CATALYST IN A REGENERTIONZONE BY CONTACTING SAME WITH A STREAM OF OXYGEN-CONTAINING GAS,RECOVERING FROM THE REGENERATION ZONE THE REGENERATED CATALYST FORRE-USE IN THE CONTACTING ZONE AND A FLUE GAS HAVING A LOWER CALORIFICVALUE THAN SAID HYDROGEN-RICH GAS, AND COMBINING THE RECOVERED FLUE GASWITH THE HYDROGEN-RICH GAS TO REDUCE THE CALORIFIC VALUE OF SAIDHYDROGEN-RICH GAS TO A VALUE APPROPRIATE TO THE USE OF THE FORMEDBLENDED GAS AS A TOWN GAS.